1. Technical Field
The present disclosure relates to magnetic resonance imaging (MRI) and, more specifically, to the automatic localization of the left ventricle in cardiac cine MRI.
2. Discussion of Related Art
Magnetic resonance imaging (MRI) is a medical imaging technique in which a human subject can be imaged in three-dimensions with a great deal of detail pertaining to the differentiation of different forms of bodily soft tissue. Thus MRI is well suited for the visualization and diagnosis of cardiovascular disease. In MRI, the human subject is exposed to a powerful magnetic field which aligns the nuclear magnetization of hydrogen atoms in water within bodily tissues. Radiofrequency fields are used to systematically alter the alignment of this magnetization and the hydrogen nuclei then produce a rotating magnetic field detectable by the scanner.
Structural image data may be generated from the received data signals to construct an image of the body. For example, the structural image may be generated from a number of spatial frequencies at different orientations. Frequency and phase encoding are used to measure the amplitudes of a range of spatial frequencies within the object being imaged. The number of phase-encoding steps performed may be selected to determine how much imaging data may be collected.
As MRI uses magnetic and radiofrequency fields to perform visualization, the patient is not exposed to potentially hazardous ionizing radiation as would be the case with CT scans.
Cardiac Cine MRI is the process by which multiple MR images are acquired in sequence over a period of time spanning one cardiac cycle. The result of cardiac cine MRI is a sequence of images that may form a moving picture showing how the heart pumps blood. Cardiac cine MRI may then be examined to assess ventricular function. For example, segmentation of the left ventricle may be used to measure the volume of blood in the left ventricle immediately before a contraction, an attribute known as the end-diastolic volume. Similarly, the volume of blood in the left ventricle at the end of contraction, an attribute known as end-systolic volume, may also be measured. The difference between end-diastolic and end-systolic volumes is the stroke volume, and represents the volume of blood ejected with each heart beat. The ejection fraction is the fraction of the end-diastolic volume that is ejected with each beat; which is the stroke volume divided by end-diastolic volume. The ejection fraction (EF) may have significant value in diagnosing cardiac disease.
According to the standard procedure for acquiring a cardiac cine MRI, the heart is imaged in three-dimensions using an MR scanner and the resulting image data is divided into short axis slices covering the left ventricle (LV) from the base of the heart to the apex. The image slices may then be analyzed using a semi-automatic segmentation tool that uses operator input to understand the structural features of the heart that are of diagnostic value, as the cardiac cycle progresses.
The level of operator input involved in performing the semi-automatic segmentation results in the procedure being time-consuming. Moreover, the quality of the results may be highly operator dependent and may be susceptible to human error.